1. Field of the Invention
This invention relates to a flow cell which is used, for example, in high performance chromatography.
2. Background Description
The term flow cell as used in this specification denotes devices for measuring the optical properties of continuously flowing liquids. These devices basically comprise an inner chamber defined on opposite sides by optical windows, and in which a liquid, that is supplied and discharged by suitable connections, is subjected to a radiation (e.g. light) for measuring purposes. There are numerous proposals for using such flow cells in various applications.
In high performance chromatography, the flow cells used in detectors--normally fluorescence or absorption measuring devices--must satisfy extreme requirements. They must withstand high pressures of up to 400 bars, have high thermal resistance, be resistant to aggressive or corrosive solvents, be fully transparent in the ultraviolet and visible range and have minimum dead volume.
One of the main problems hitherto was the seals or gaskets, which usually consist of polytetrafluoroethylene, known by the name Teflon, a material which although it extensively satisfies certain of these requirements does not do so completely. In particular, the space alongside the seal including the liquid creeping between seal and solid surfaces forms dead volumes which result in remixing and must therefore be negligibly small in relation to the cell volume to avoid incorrect readings. Their existence limits the minimum value of possible cell volumes. The problem of dead volume hitherto was not solved in the optimum way.
If the cell were made of a material such as metal having low thermal resistance, there is an additional problem that thermal instability between the pulsating liquid and the metal cell walls gives rise to refractive index fluctuations which finally result in interfering fluctuations (noise) of the measurement signal.